At present, nano-order micro-particles are greatly demanded in a variety of industrial fields, and dispersion technologies of the nano micro-particles are regarded as critical. Among them, a major technical hurdle to a stable dispersion technology of inorganic micro-particles in a solvent-based resin has surfaced. That is, because the surface of inorganic micro-particles is generally hydrophilic, it is generally said that producing a solvent-based dispersion is quite difficult. To overcome the above problem, for example, to disperse hydrophilic inorganic micro-particles in a solvent, a dispersion technique in which a hydrophobic dispersant is supplied as a protective colloid via a chemical bond on the micro-particle surface, is disclosed, for example, Patent Document 1. However, in Patent Document 1, not mentioned nor at all indicated on a solvent-based micro-particle dispersion technology of applying a hydrophobic dispersant compared to hydrophilic protective colloid particles, which are dispersible in a water system.
Further, as a dispersion method in a hydrophilic-lipophilic dispersion system, a method, in which thermosensitive polymers capable of reversibly varying hydrophilicity/hydrophobicity by making a transition temperature of a dispersant polymer as a threshold value, which is disclosed, for example, Patent Document 2. However, since it the method disclosed in Patent Document 2, hydrophilicity/hydrophobicity of a dispersant polymer is reversible by temperature, it is problematic that a significant limitation will result with respect to modification variations in a water system and a solvent-system, respectively.
That is, this invention is characterized in that nano-order micro-particles are dispersible in both a water system and a solvent system. To enable micro-particle modification in a water system, and separately in a solvent system, in each liquid phase is a quite new technique, and can be said to be a technique having a great advantage and promising potential.
On the other hand, in recent years, in the medical and printing plate making fields, a decrease in processing effluent, resulting from wet type processing of image forming materials, has been highly demanded, from the viewpoint of environmental protection as well as storage space conservation. Accordingly, technologies related to a silver salt photothermographic dry imaging material (hereinafter, also referred to as a photothermographic material or a photosensitive material) to be applied in photographic technology, which can perform efficient exposure such as a laser imager and a laser image setter as well as a black colored image formation having high resolution and sharpness, have been required.
As technologies concerning the above photothermographic material, such as described for example in U.S. Pat. Nos. 3,152,904 and 3,487,075, by D. Morgan and B. Shely, or in “Dry Silver Photographic Materials” (Handbook of Imaging Materials, p. 48, 1991, published by Marcel Dekker Inc.), a silver salt photothermographic dry imaging material, which contains an organic silver salt, a photosensitive silver halide emulsion and a reducing agent on a support, is prior art. This silver salt photothermographic dry imaging material has the advantage of providing operators with simpler handling and minimal environmental disturbance since no solution type processing chemicals are at all employed.
These silver salt photothermographic dry imaging materials are characterized by utilizing photosensitive silver halide grains as a optical sensor and organic silver salt as a supply source of silver ion, and performing image formation, by use of an integral reducing agent, by thermal developing generally at 80-140° C., without fixing.
In silver salt photothermographic dry imaging materials such as in particularly described above, in a silver salt photothermographic dry imaging material prepared by a solvent type coating method, a silver halide emulsion utilized as a photoreceptor often utilizes a hydrophilic dispersant such as gelatin as a protective colloid, often resulting in a problem of causing grain aggregation or unnecessary grain growth (also referred to as ripening) when silver halide grains are exposed to an organic solvent. However, since there are many advantageous conventional technologies due to utilization of gelatin as a protective colloid, such as a silver halide grain forming technology using a water medium, a chemical sensitization technology of silver halide grains by a water-soluble sensitizer, a storage technology of silver halide grains using a gelation of gelatin, problems such as aggregation of silver halide grains in a solvent system had to be compromised to some extent.
Heretofore, as conventional counter-measures to grain aggregation, silver halide grains are added during formation of organic silver salt grains, which are contained in a silver salt photothermographic dry imaging material, to utilize a long-chain fatty acid as a dispersant for silver halide grains, resulting in reduced aggregation. However, dispersibility of silver halide grains is not sufficient, as well as fogging, which is an important characteristic in a silver salt photothermographic dry imaging material, because of a mixed system with organic silver salts, that is, it is the present state of the art which problems have not yet been overcome.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 5-111631
[Patent Document 2] JP-A 7-276792